I really would not recommend really modifying those tires much. It looks like they have a tendency to disintegrate a lot and really do not stop if they start too.

That was Team 1135, Whitney High Shmoebotics. It took them a while to get going but they did well in the end.

Tank drive is the way to go, as a rookie team last year we can attest that it did wonders for us.

a) It is easy to assemble. Just attach the drill motor assemblies to a frame, add a sprocket and a few chains... voila!

b) It provides both power and precise control. Lets face it... CASTERS SUCK! How many teams last year with casters didn't have trouble making it up the ramp? Not many :(

c) Easy to add upgraded functionality. We just happened to add a servo gear shifter so we could be fast, or powerful.

Here is a pic of what our base looked like last year. Very simple square base with a two beams running in the center to hold the drills.

In my limited experience with those tires, I've found them to be resilient. Obviously, the wire mesh of the 2003 game was a special circumstance that was destructive to all sorts of tires.

Turned down on a lathe, those wheels seem to provide adequate, accesible traction. Also, they come in the kit and they're keyed.

One more reason to go with extrusion is than you can slide the pillow blocks for chain tension adjustment. We would have been in major trouble without that. Another substitute is an adjustable or sring loaded idler sprocket to use as a tensioner if extrusion is not used.

You can also do the same thing with square tube but you woyuld have to have slots milled.

You could also make those same slots with a drill press and a Dremel. I would know; we've done it for OCCRA, which doesn't allow milling machines. I would only advise it on aluminum, though... we burned out a dremel doing it on steel.

Well, that's precisely why I don't like extrusion. The fasteners aren't terribly secure and can slide all over the place inside the t-slots. When you need to keep things in line or in certain spots, extrusion makes it harder.

While you can tension chain easily by sliding things around, those same things sliding around during a match can throw chains. I have first hand experience with that.

You don't need a different material, just a stronger arm on whoever installs the hardware and a little Lock-Tite too.

The Slam Hammer's your friend..

http://www.chiefdelphi.com/forums/pi...gle&picid=3546

This is what killed us this season.
Never again.

Helical Gears
 

One thing to keep in mind about the "ready made" chassis. 90° helical gears are MUCH less efficient than straight spur gears or even chains. Since we all have to play with the same motors and the same power sources, efficiency is the name of the game in FIRST robotics.

I would recommend for a rookie team to chain drive the wheels to an intermediate shaft and use the FIRST provided coupler to attach the Bosch Tranny/Motor to the end of the intermediate shaft.

MattB
902

They are resilient just make sure you are:
A) Really careful in modifying them
B)Make sure those tires do not become damaged.
Once the tires become damaged they are really just shot. The rubber on those things disintegrates fairly easily.
Actually the first season I was in the robot rolled off the table. The only thing that was wrong with the frame afterwards was that the wheels were off a bit but that was due to our innept drilling skills more than dropping it off a table. Plus I am pretty sure reading about using a torsion wrench to tighten the nuts which I am fairly certain that not a lot of teams do.

For this reason, I'm also trying to make replacing the wheels a simple process. In fact, as I have it, you can replace the entire wheel/key/axle/sprocket assembly with a new one.

Quote:

Actually the first season I was in the robot rolled off the table. The only thing that was wrong with the frame afterwards was that the wheels were off a bit but that was due to our innept drilling skills more than dropping it off a table. Plus I am pretty sure reading about using a torsion wrench to tighten the nuts which I am fairly certain that not a lot of teams do.

Well, in addition to the fasteners sliding around, another problem is pulling them straight out of their slots by tension. Overtightening them risks making this happen more frequently.

We had the same problems as everyone else with the extrusion and T-slots so we make it a habit of using t-nuts to prototype with then when things are where we want them drill through the extrusion and bolt the piece where you want it.

We ended up tapping the ends of the extrusion and attaching everything from there.